1. Field of the Invention
The present invention relates to an organic EL device and, in more detail, it relates to an organic EL device comprising, between a cathode and an anode, a hole transporting layer and an organic luminescent layer which comprises an organic compound.
2. Description of the Related Art
As shown in FIG. 5, a conventional two layer type EL device having, between a cathode 100 and an anode 104 formed on a glass plate 102, a luminescent layer 108 composed of a luminescent material which exhibits electroluminescence when a voltage is applied thereto and a hole transporting layer 106 which transports holes generated in the anode 104 smoothly to the luminescent layer 108, has been used in a backlight for the display of an OA machine such as a word processor, for an automobile meter, and the like.
Although an inorganic compound has conventionally been used as the luminescent material for such an EL device, a high driving voltage has been required when the inorganic compound for the EL device is caused to emit high-intensity light.
Accordingly, research on organic luminescent compounds for EL devices which allow lower driving voltages has recently been conducted (see, for example, C. W. Tang and S. A. VanSlyke: Appl. Phys. Lett. 51. 913 (1987)).
An organic EL device having a luminescent layer composed of such an organic compound can be driven at a low voltage compared with an EL device having a luminescent layer composed of a conventional inorganic compound.
However, such a conventional organic El device does not emit light of a sufficient intensity when used in a backlight for a display of an OA machine, and the like.
Although Japanese Unexamined Patent Publication No. 8-81472 discloses a three layer type EL device having a luminescent layer composed of 2-(O-hydroxyphenyl)-benzoxazole or -benzothiazole zinc complex, a three layer type organic EL device having an electron transporting layer composed of such a zinc complex as mentioned above has not been known.